Industrial production of hydroxybenzyl alcohols has conventionally been carried out by reaction between phenol with formaldehyde in the presence of a basic catalyst without a solvent. Rarely has the reaction been effected in a nonaqueous solvent.
Known processes for obtaining p-hydroxybenzyl alcohol on an industrial scale include a process comprising reacting phenol and formaldehyde to obtain a mixture of p-hydroxybenzyl alcohol and o-hydroxybenzyl alcohol and separating the mixture into each isomer by, for example, extraction as disclosed in JP-A-54-36223 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
In the reaction between phenol and formaldehyde in the presence of a basic catalyst, a production ratio of p-hydroxybenzyl alcohol to o-hydroxybenzyl alcohol (hereinafter referred to as para/ortho production ratio) is generally no higher than 1.0.
Techniques so far proposed for increasing the production ratio of p-hydroxybenzyl alcohol in the reaction between phenol and paraformaldehyde include (1) addition of a polyalkylene ether to the system containing a strongly basic catalyst as disclosed in JP-A-56-16423 and (2) use of an organic nitrogen compound having at least two nitrogen atoms per molecule as a basic catalyst as disclosed in JP-A-56-16424. Nevertheless, the proportion of the para-compound in the resulting mixed hydroxybenzyl alcohol as obtained by these processes is still lower than that of the ortho-compound, i.e., 49% and 47%, respectively.
It has recently been proposed to selectively synthesizing p-hydroxybenzyl alcohol using cyclodextrin and modified cyclodextrin as reported in J. C. S., p. 652, c.c. (1988). According to this process, .beta.-cyclodextrin, sodium hydroxide, and formaldehyde are used in amounts of from 20 to 40 times, 50 times, and 40 times, respectively, the amount of the starting phenol. Therefore, although the para/ortho production ratio reaches 15.7, the process is of no industrial advantage from the economical standpoint.